The Obama campaign e-mailed collections of the criticisms and video links to reporters and supporters, and updated a “Truth Team” feature on its Web site. Top advisers said they would seek to make the Republican candidates’ statements into a larger issue of character, one that they hoped would reinforce Mr. Romney’s image among many voters as a shape-shifting politician who has reversed position on abortion and gay rights, gun control and other issues — as his Republican rivals complained throughout their long nomination battle.

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What is unclear is whether the Romney-Ryan ticket will pay a political price. In response to the criticism, a campaign spokeswoman, Andrea Saul, said late Thursday, “President Obama and his team are running a campaign of personal destruction to avoid talking about his failed economic record.”

Criticism from the Obama campaign could well be dismissed among voters as the usual stuff of politics, and independent fact-checkers have criticized some of Mr. Obama’s statements, too. Still, the number of falsehoods and misleading statements from the Romney campaign coming in for independent criticism has reached a level not typically seen.

“The Romney campaign has, as is strikingly evident at the Tampa convention, broken new ground in its brazen and cynical disregard for the truth,” said Thomas E. Mann, a longtime political scholar at the center-left Brookings Institution and co-author of the recent book about politics, “It’s Even Worse Than It Looks.”

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Mr. Romney and Mr. Ryan, he added, are “counting on a mainstream press, fearful of being charged with partisan bias, of shrinking from their responsibility to report the truth.”

Mr. Obama this week, for the first time, entered the fray. Campaigning on Tuesday on college campuses in Iowa and Colorado, he told thousands of supporters not to believe the opposition’s attacks because, “how do I put this nicely? They will just fib.” On Wednesday in Charlottesville, Va., he ramped up his complaint, winning applause from the estimated 6,500 people.

“Sometimes they just make things up. But they’ve got a bunch of folks who can write $10 million checks, and they’ll just keep on running them,” he said. “I mean, somebody was challenging one of their ads — they made it up — about work and welfare. And every outlet said this is just not true. And they were asked about it and they said — one of their campaign people said, ‘We won’t have the fact-checkers dictate our campaign. We will not let the truth get in the way.’”

Mr. Obama was referring, as many other critics of the Romney campaign have, to a comment that its pollster, Neil Newhouse, made to reporters at the Republican convention on Tuesday, dismissive of those faulting the campaign’s television ads. What Mr. Newhouse actually said was, “These fact-checkers come to those ads with their own sets of thoughts and beliefs. We’re not going to let our campaign be dictated by fact-checkers.”

Mr. Newhouse did not say, “We will not let the truth get in the way.”